Distillation of benzene fractions with butyraldehyde



March 9, 1943. R, B, GREENBURG 2,313,536

DISTILLATION OF BENZENE FRA'CTIONS WITH BUTYRALDEHYDE Filed July 12,1941 Condenser INVENTO'R /fzfafd 5. reena@ ATTORN EY Patented Mar. 9,1943 DISTILLATION F BENZENE FRACTIONS WITH BUTYRALDEHYDE RichardGreenburg, Philadelphia, Pa., assigner, by mesne assignments, to AlliedChemical & Dye

Corporation Application July 12, 1941, Serial No. 402,143

9 Claims.

This invention relates to a process for recovering benzene from mixturescontaining it and other hydrocarbons.

Numerous hydrocarbon oils are known which contain benzene in varyingproportions. Gasoline fractions obtained by the distillation of certaintypes of petroleum or recovered from the products of catalyticreformation processes, frequently contain substantial proportions ofbenzene, although mainly consisting of other hydrocarbons. Oils ofpetroleum origin having a considerable content of aromatics, includingbenzene, may be treated by well known selective solvent processes toproduce fractions rich in aromatics; for example, extraction of suitablefractions of suchpetroleum oils with sulfur dioxide may yieldfractionsof high benzene content. In such cases benzene is accompaniedby nonaromatic hydrocarbons which may be largely oleiinic, paraiiinic,or naphthenic in character. A considerable proportion of thesehydrocarbons cannot be completely separated from the benzene by directfractional distillation because of the closeness of their boiling pointsto that of benzene or because they form constant boiling mixtures withbenzene. Furthermore, while ordinarily benzene is readily separable bydirect fractional distillation from light oils produced by thegasification of coal, in some cases the benzene is accompanied bydiflicultly separable non-aromatic hydrocarbons of the same generalcharacter 'as described, owing to carbonization conditions, type of coalused or other special circumstances. Also synthetic hydrocarbon oilmixtures produced by various catalytic processes may contain benzenewhich, when recovered, is accompanied by `similar diiiicultly separableconstituents.

By fractional distillation of these oils containing benzene, fractionsrelatively high in benzene content may be obtained. These benzenefractions, however, will still contain large amounts of the otherconstituents of the oil having boiling points in the neighborhood of theboiling point of benzene or forming mixtures of constant boiling pointsin the range of temperatures at which benzene distills from the oil. (Inthis specification and claims, I refer to such diicultly separableconstituents, which distill out over the same temperature range as thebenzene and from which the benzene is not separable by a consourcespresents a diiiicult problem of great industrial importance.

For many purposes to which benzene is put, it is desirable to use aspure a material as may be economically available. For example, benzeneis used for the production of pharmaceutical chemicals, dyes andsynthetic phenol. For these purposes a pure benzene is preferred. Directfractional distillation, because of the difculties pointed out above,will not effect a recovery of pure benzene separate from like-boiling,nonaromatic hydrocarbons such as enumerated, and in many cases willnotgive fractions of suitably high benzene content or free from materialswhich even in small concentrations adversely af. fect the processes bywhich the benzene is treated or the products produced therefrom.

It is an object of my invention to provide a process whereby benzene ofany desired degree of purity may be recovered from hydrocarbon oilmixtures comprising non-aromatic hydrocarbons from which the benzene isnot separable by a conventional distillation.

In using my invention for the treatment of an oil in which the benzeneconcentration is low or when the oil is one containing materials of wideboiling range, I prefer first to fractionally distill the oil to recovertherefrom an enriched benzene fraction. Although benzene`fractionshaving an end boiling point substantially above the boiling point ofbenzene (e. g., a boiling point up to about 85 C.) may be azeotropicallydistilled in the manner hereinafter described, I prefer the benzenefraction treated by my process to be one having an end boiling pointsubstantially corresponding to the boiling point of pure benzene, e. g..an end boiling point of about 80 C. Further, for the reasons which willbe more specifically pointed out below, I prefer that a benzene fractionrecovered by a preliminary distillation of a crude benzene oil be so cutas to exclude therefrom the forerunnings which do not containsubstantial proportions of benzene; for example, to exclude substantialproportions of oils distilling below C.

In this specication and claims, the term benzene fraction is usedbroadlyto designate any oil fraction containing both benzene and otherhydrocarbons which, under the conditions maintained in directdistillation processes as commonly used for distilling oils, distillfrom the fraction within the same temperature range as does the benzene.

I have discovered that benzene may be"sep arated from a benzene fractionsuch as described above by subjecting it to azeotropic distillation inthe presence of butyraldehyde, either normalor iso-butyraldehyde. Thenon-aromatic hydrocarbons. which in the absence ofthe butyraldehydedistill from the benzene fraction in the same temperature range as thebenzene and hence are not separable therefrom by direct fractionaldistillation, may be distilled from the benzene fraction in the presenceof the butyraldehyde to leave a residue containing benzene of anydesiredv purity with respect to its content of these like-boiling,non-aromatic hydrocarbons. On fractionally distilling a mixture of thebutyraldehyde with a benzene fraction, the material first to distillover is a mixture of low-boiling azeotropes `consisting chiefly ofbutyraldehyde and non-aromatic hydrocarbons (together with water ifpresent). On continued distillation, the non-aromatic hydrocarbons areselectively removed and a residue enriched in benzene is` obtained.'I'he distillate will contain butyraldehyde and the nonaromatichydrocarbons distilled from the benzene fraction. It may containbenzene, the amount depending on the effectiveness of fractionation.

The azeotropic distillation may be carried out either under anhydrousconditions or in the presence of substantial quantities of water. Whenwater is present a part or all of the water, depending upon the quantitypresent, is carried over in the distillate as an azeotrope of the water,butyraldehyde and nonaromatic hydrocarbons.

Water appears to aid in the production of a pure Y benzene product. Bywashing the distillate with an aqueous solution of sodium acid sulfitethe butyraldehyde in the distillate may be separated in an aqueous phasefrom an oil phase containing the hydrocarbons carried over into thedistillate. The aqueous phase may be treated to recover butyraldehydetherefrom for return to the distillation and reuse in the azeotropicdistillation of additional benzene fraction. Butyraldehyde which may beleft in the residue may be removed by washing the residue with sodiumacid sulfite solution. The oil phase thus obtained, containing benzenewhich has been separated from non-aromatic hydrocarbons in the originalbenzene fraction, may then be washed with caustic soda solution toremove any sulfur dioxide present and, if desired, may be given aconventional acid wash and redistillation to further purify the benzene.

My invention comprises, therefore, azeotropically distilling in thepresence of butyraldehyde a benzene fraction containing non-aromatichydrocarbons which distill from said fraction in the absence o anazeotropic agent, in the same temperature range as the benzene, e. g.,hydrocarbons which normally boil from mixtures thereof with benzenebetween and 80 C. and from which the benzene is not readily separable byconventional distillation.

The azeotropic distillation in the presence of the butyraldehyde shouldbe carried out with effective rectification of the vapors. Sufficientbutyraldehyde should be present ,to carryover as azeotropes thenon-aromatic hydrocarbons so that the residue containing benzene isfreed to the desired degree of these non-aromatic hydrocarbons. Thequantity of butyraldehyde thus required will, of course. depend upon theamount of benzene fraction distilled, the quantity of nonaromatichydrocarbons contained therein, etc. Any excess of butyraldehyde presentwill not materially interfere with the separation of the non-aromatichydrocarbons from the benzene,

although it is obvious that a large excess is undesirable in that itrequires removal and recovery of the butyraldehyde from the benzeneproduct of the process.

As pointed out above, it is highly desirable to recover from benzenefractions a relatively pure benzene product and the process of myinvention permits of obtaining an enriched benzene residue of anydesired purity with respect to hydrocarbons which, in the absence of anazeotropic agent, distill from the benzene fraction in the sametemperature range as the benzene. My invention contemplates, therefore,continuing the azeotropic distillation of the benzene fraction under theconditions described above until the distillation residue is enriched toa desired extent in benzene with respect to other like-boilinghydrocarbons; i. e., hydrocarbons which will distill from the benzenefraction, in the absence of an azeotropic agent, in the same temperaturerange as the benzene distills therefrom. In practicing my invention therectication preferably is controlled to obtain a benzene residue whichcontains at least 90 parts by weight of benzene to Il; parts oflike-boiling, non-benzene hydrocar- The benzene fraction treated inaccordance with my invention preferably will contain little, if any,hydrocarbons distilling from the hydrocarbon-benzene fraction attemperatures materially above those at which benzene distills therefrom.On the other hand, a small amount of high boiling materials may be leftwith the benzene residue at the conclusion of the azeotropicdistillation of the benzene fraction under the conditions set forthabove to separate the benzene from the hydrocarbons of similar boilingrange. Once this separation has been effected, the benzene may beseparated from the high boiling hydrocarbons by fractional distillationin the absence of an azeotropic agent. Whether or not high boilingconstituents should be left in the benzene fraction to be azeotropicallydistilled or whether, if left in the benzene fraction, they will remainin the residue after azeotropic distillation, depends upon a number offactors, among which their boiling range and chemical characteristicsare important. If the high boiling constituents form azeotropes with theagent used which have D boiling points close to the temperatures atwhich benzene distills over, it is preferable to separate such highboiling constituents from the benzene fraction by a direct fractionaldistillation before azeotropicaily distilling the benzene fraction.

When pure benzene is to be recovered itis preferred the benzene fractionsubjected to azeotropic distillation in accordance with my invention bea fraction boiling within the range of 65 C. to C. Such a fraction maybe azeotropically distilled by my process and pure benzene obtained witha relatively small quantity of azeotropic agent present during thedistillation. Pure benzene may be obtained by distilling with anazeotropic agent a wider boiling benzene fraction but the quantity ofazeotropic agent present in the distillation of the benzene fraction ofwider boiling range must be substantially increased as compared with thequantity which suices for distilling the fraction of the narrowerboiling range.

Benzene of high purity is desired for nitration and other purposes andthe process of my invention provides a method whereby a pure benzene ofnitration grade may be economically recovered from benzene oils. Theinvention, however, is not limited thereto. Benzene products of lowerpurity than nitration grade benzene are industrially .used for variouspurposes, e. g., as solvents. The process of my invention may be usedadvantageously for recovering such products from hydrocarbon oils oflower benzene content. My process is particularly advantageous when thebenzene is to be separated from most of the like-boiling, nonaromatichydrocarbons present in an oil fraction together with benzene, e. g.,when a product is to be obtained containing benzene and no more than 10parts by weight of like-boiling, non-aromatic hydrocarbons for every 90parts by weight of benzene.

My invention will be more particularly described and illustrated by thefollowing examples of processes for the azeotropic distillation of abenzene fraction `in the presence of butyraldehyde.

The apparatus used for carrying out the process of these examples,diagrammatically illustrated in the accompanying drawing, comprised astill l with heater 2 and rectification column 8 of conventional design,the rectification column containing suicient liquid-vapor contactelements for it to effectively fractionate the vapors evolved in thestill and passed therefrom through the rectification column. A condenserl was provided to which the vapors from the top of the column were ledand in which they were cooled and condensed. A pipe 5 was provided forreturning condensate from the condenser to the top of the rectificationcolumn to serve as reux for the column. A second pipe 6 was alsoprovided for drawing off from the condenser a portion of the condensateformed therein. Pipes l and 8 are provided for the introduction ofliquids into still l. A pipe 9 serves for withdrawal of residue fromthis still.

Example 1.-The above-described apparatus was employed for thedistillation of a benzene fraction having a boiling range of about 75 C.to

about 80 C. and containing 69% by volume of benzene. the remainderprincipally consisting of like-boiling parains. 'i

100 volumes of this benzene fraction, 100 vol'- umes of N-butyraldehyde,and 10 volumes of water were charged into the still of the apparatusdescribed abc-ve. This charge was boiled in the still and the vaporspassing therefrom to the fractionating column were. rectiiied in thiscolumn. The vapors leaving the tcp of the column were condensed, a partof the condensate was withdrawn as distillate through pipe 6, and theremainder of the condensate returned as reflux through pipe 5 to the top0f the fractionation column. Distillation started with the temperatureof the vapors at the top of the fractionation column at about 57 C. and,as the distillation proceeded, the temperalture rose to 67 .4J C. Aftertaking 01T through pipe 6 a total of 125 volumes of distillate and withthe temperature at the top of the column at 67.4 C., a residue of '76volumes was left in still l. Ihis residue was washed with a solution ofsodium acid suliite, followed by washing with caustic soda solut-ion andthe oil separated from the aqueous solutions was analyzed for benzene.This oil was found-:to contain 98% benzene by the specific dispersionmethod for its analysis described in Industrial & Engineering Chemistry,analytical edition, vol. 11, page 614, November 15, 1939. By theKattwinkel Method of Analysis, Brennstoff- Chem., vol. 8. page 3531927), it was shown as 100% benzene.

The process of this example may be modified to carry out thedistillation of the benzene fraction and butyraldehyde undersubstantially anhydrous conditions; i. e., without adding to the stillcharge azeotropic distillation of the benzene fraction. In

this example 100 volumes of the benzene fraction containing 69% benzene,100 volumes of isobutyraldehyde, and 10 volumes of water were chargedinto still i and distilled with rectification ol' the vapors in column3, condensation of the distillate and return of a portion of thedistillate as reflux to column 3, with the remaining portion beingwithdrawn through pipe 6. In this case distillation started at atemperature of about 48 C.

and, when a total of 125 volumes of distillate had been taken ofithrough pipe 6, the temperature had risen to 62.5 C. The residue of 73volumes was washed with sodium acid sulte and caustic sro-da solutionsand the oil layer thus obtained analyzed 98% benzene by the specificdispersion method and 100% benzene by the Kattwinkel Lil method.

The procedure of this Example 2 may likewise be modified to carry outthe distillation of the benzenefraction under substantially anhydrousconditions. Thus, a charge of volumes of the benzene fraction and 100volumes of isobutyraldehyde introduced into still I was distilled.Distillation started with the temperature oi the vapors at thetop of thefractionation column at about 50 C. and, as the distillation proceeded,the temperature rose until, when volumes distillate had been taken offthrough pipe the vapors at the top of the column were at 78.9 C. The.residue in the still, amounting to 63 volumes, was washed with sodiumacid sulte and caustic soda solutions to give an oil which analyzed atleast 93% benzene.

While both of the examples described above employ a batch operation forthe distillation of the benzene fraction, this distillation may becarried out continuously. For example, butyraldehyde and benzenefraction may be continuously supplied to a column still in which thebenzene is concentrated and, flowing to the bottom of the still, iscontinuously lwithdrawn therefrom. The azeotropes of' butyraldehyde andnonaromatic hydrocarbons are continuously vaporized and withdrawn asdistillate from the top of the distillation column. Suicientbutyraldehyde should be supplied to carry over as distillate all of thehydrocarbons to be distilled from the benzene fraction and separatedfrom the benzene. By observation of the vapor temperatures at a suitablepoint in the vapor rectification column, one may ascertain whetheradequate butyraldehyde is present. Whenever these vapor temperaturestend to exceed 76 C. for normal-butyraldehyde and 64 C. forisobutyraldehyde under anhydrous conditions, or 671/2" C. fornormal-butyraldehyde and 60 C. for isobutyraldehyde when water ispresent before the benzene has been separated to the desired degree fromthe like-boiling, non-aromatic hydrozene and like-boiling, non-aromatichydrocarbons may be accomplished. This point of temperature observationin the apparatus in which the above examples of the process were carriedthermore, the distillation may be carried out as a continuous procedureinstead of the batch procedure described above. In a continuouslyoperating process enriched benzene products may be taken off from thebottom of the still or as one or more side streamsfrom the fractionationcolumn below the point of feeding the benzene fraction thereto. Thesemodifications are within the scope of my invention.

In this specification I have described the azeotropic distillation asbeing carried out under substantially atmospheric pressure. Thetemperatures as given herein are corrected temperatures for 1 atmosphereabsolute (760 mm. of Hg). When carried out under pressures other thanatmospheric, the temperature conditions will diil'er from those given.In any given case, however, the temperatures will correspond to thechange in boiling points ofthe materials due to the diiference inpressure.

I claim:

1. The process for the recovery of benzene form a benzene fractioncontaining the same and containing a mixture of like-boiling,non-aromatic hydrocarbons which comprises distilling said benzenefraction and rectifying the distilled vapors in the presence ofbutyraldehyde in an amount which selectively carries over' as distillatesaid like-boiling, non-aromatic hydrocarbons and leaves a hydrocarbonresidue of the distillation enriched in benzene.

2. The process for the recovery of benzene which comprises distilling abenzene' oil fraction boiling within the range of 65 C. to 80 C. andcontaining benzene and a mixture of like-boiling, non-aromatichydrocarbons and rectifying the distilled vapors in the presence ofbutyraldehyde which selectively carries over as distillate saidlike-boiling, non-aromatic hydrocarbons and leaves a hydrocarbon residueof the distillation enriched in benzene.

3. The process for the recovery of benzene from a benzene fractioncontaining the same and containing a mixture of like-boiling,nonaromatic hydrocarbons which comprises distill- 'ing said benzenefraction in the presence of butyraldehyde and water, said butyraldehydebeing present in an amount which selectively carries over as distillatesaid like-boiling, nonaromatic hydrocarbons and leaves a hydrocarbonresidue of the distillation enriched in benzene.

4. The process for the recovery of benzene from a benzene fractioncontaining the same and containing a mixture of like-boiling,nonaromatic hydrocarbons which comprises distilling said benzenefraction and rectifying the distilled vapors in the presence ofnormalbutyraldehyde in an amount which selectively carries over asdistillate said like-boiling, nonaromatic hydrocarbons and leaves ahydrocarbon residue of the distillation enriched in benzene.

5. The process for the recovery of benzene from a benzene fractioncontaining the same and containimg a mixture of like-boiling,nonaromatic hydrocarbons which comprises distilling said benzenefraction and rectifying the distilled vapors in the presence ofnormal-butyraldehyde and Water, said butyraldehyde being present in anamount which selectively carries over as distillate said like-boiling,non-aromatic hydrocarbons and leaves a hydrocarbon residue of thedistillation enriched in benzene.

6. The process for the recovery of benzene from a benzene fractioncontaining the same and containing a mixture of like-boiling,non-aromatic hydrocarbons which comprises distilling said benzenefraction and rectifying the distilled vapors in the presence ofnormal-butyraldehyde, said butyraldehyde being present in amount suchthat at a point in the fractionation of the vapors evolved in distillingthe benzene fraction the temperature does not exceed '76 C. foranhydrous conditions and does not exceed ST1/2 C. when water is presentuntil said like-boiling, non-aromatic hydrocarbons have been vaporizedleaving a hydrocarbon residue of the distillation containing benzene andno more than 10 parts by weight of like-boiling, non-aromatichydrocarbons for every 90 parts by weight of benzene.

'7. The process for the recovery of benzene from a benzene fractioncontaining the same and containing a mixture of like-boiling,non-aromatic hydrocarbons which comprises distilling said benzenefraction and rectifying the distilled vapors in the presence ofiso-butyraldehyde in an amount which selectively carries over asdistillate said like-boiling, non-aromatic hydrocarbons and leaves ahydrocarbon residue of the distillation enriched in benzene.

8. The process for the recovery of benzene from a benzene fractioncontaining the same and containing a mixture of like-boiling,non-aromatic hydrocarbons which comprises distilling said benzenefraction and rectifying the distilled vapors in the presence ofiso-butyraldehyde and water, said butyraldehyde being present in anamount which selectively carries over as distillate said like-boiling,non-aromatic hydrocarbons and leaves a hydrocarbon residue of vthedistillation enriched i.i benzene.

9. The process for the recovery of benzene from a. benzene fractioncontaining the same and containing a mixture of like-boiling,nonaromatic hydrocarbons which comprises distillihg said benzenefraction and rectifying the distilled vapors in the presence ofiso-butyraldehyde, said butyraldehyde being present in amount such thatat a point in the fractionation `of the vapors evolved in distilling thebenzene fraction the temperature does not exceed 64 C. for anhydrousconditions and does not exceed 60 C. when water is present until saidlikeboiling, non-aromatic hydrocarbonshave been vaporized leaving ahydrocarbon residue of the distillation containing benzene and no morethan 10 parts by weight of like-boiling, non-aromatic hydrocarbons forevery parts by weight of benzene.

RICHARD B. GREENBURG.

- cmIFIcATE oF connac'rron.- 5 Patent No. 2,515,556. mmh 9, 1945.

` RICHARD B.` GREENBURG.

It is'hereby certified that error appears in the printed specificationof the above nmbered patent requiring correction as follows: Page firstcolumn', line 57, claim 1, for "form" readnfromn; line 51, claim2,;after the word "of" insert --a quantity of-; line 60, Aclaim 5, afterthe wordl 'fraction' insert --and rectifying the distilled vapors-u;vand that the said Letters -Pate'nt should be read withthis correctiontherein that the same may conform to the record of the case in thePatent Office.

signed and sealed this 18th day` of my, A. n. 1915,.

Henry` Van Arsdaie, (Sea1Y) I A Acting .Commissioner of Patents.'

